This invention relates to an apparatus for making an open cord, comprising a plurality of steel wires with spaces therebetween, which is used as a reinforcement for rubber goods such as automobile tires, conveyor belts, high pressure rubber hoses, etc.
A conventional steel cord 3 to be used as reinforcement of rubber goods is made by intertwisting a plurality of steel wires 1 as shown in FIG. 1 (a) and FIG. 1 (b). In FIG. 1 (b) numeral 2 denotes a core strand. However, since such conventional steel cord 3 comprises several steel wires 1 which are in tight contact with each other, when the cord is covered with a rubber compound, such rubber compound will not penetrate into the core and as a result, adhesion between each steel wire 1 of the steel cord 3 and the rubber compound is imperfect. Thus, the conventional steel core cannot perform its duties fully as a reinforcement. For example, when the conventional steel cord is used as a reinforcement for automobile tires, such trouble as the rubber compound separating from the steel cord or the so-called "separation phenomenon" is caused during operation, which results in impairing the function of the tires considerably. Moreover, since the rubber does not penetrate into the core of the steel cord, a space is present at the core and humidity in the rubber, humidity in the atmosphere, etc. penetrate into such space, with the result that the steel wires gather rust easily and such rust spreads rapidly all over the steel cord, causing a sharp reduction of steel cord the strength of the, breakage of the steel cord and above mentioned "separation phenomenon".
In order to eliminate the above-mentioned disadvantages, it has been proposed to put to practical use a such steel cord having loosely intertwisted steel wires, or the so-called open cord, which is made by intertwisting several steel wires 1 with spaces left therebetween as shown in FIG. 3 (a) and FIG. 3 (b). However, no practical apparatus for manufacturning such above-mentioned steel cord of such soft twist, no has yet been developed. The only method under consideration is to use a wire stranding machine of tubular type, whereby each steel wire is curled excessively by a conventional cone pin. According to this method, however, the steel cord 3a with loosely twisted wires easily becomes unstable during twist construction, the steel wires 1 become one-sided as shown in FIGS. 2 (a), (b) and (c), and the twist becomes uneven in lengthwise direction of the cord. In an case of the open cord having such one-sided wires and unevenness of twist, even if the rubber compound penetrates into the core of the open cord, the cord is reduced in strength, has an extremely poor compression flexing fatigue characteristic, and cannot be used as a reinforcement for rubber goods.